Bridget Jones is back, no longer, obviously, in her thirties but 51 — answering to 35. So far, so good. But in the intervening 14 years something happened, and not just her marriage (Bridget as Mrs Darcy is a bit of a shock), her two children, nor indeed her widowhood or her discovery of Twitter. In Mad About the Boy, she’s changed. She’s not Everywoman any more, not the way she was first time round, though she’s still funny and there are bits you can still identify with (like only having one dress that you can actually wear notwithstanding a stuffed wardrobe).

The initial reviews have not been happy. “Reading the first two-thirds of Mad About the Boy is like listening to someone who once had perfect pitch, but now can’t sing a note,” observed the Telegraph. “This brand … seems to have lost its shine,” said the Sunday Times.

What went wrong? If you had to put your finger on the chief ways Bridget has changed you could sum them up in two words: sex and money. Too much of both.

Bridget in her old incarnation never had any hang-ups about sex, apart from those associated with body-image. She was merrily Up for It. But although she’d sleep with Daniel Cleaver and Mark Darcy — indeed in a little excursion in The Independent before this book she was unable to work out which fathered her baby — there wasn’t anything graphic about it. Daniel Cleaver tearing her clothes off, yes; Mark Darcy carrying her to the four-poster, of course; but not much in the way of actual detail.

So, how do we take the following: “Oh God. What was I thinking having sex all night? The whole makeup/breakup thing somehow whipped Roxster and me up into a sexual frenzy and neither of us could stay asleep. Was actually hanging upside down from the side of the bed with Roxster holding both my legs in the air whilst thrusting in between them when suddenly — ” And that’s not the worst. The culminating sex scene, the one that confirms that she is indeed with The One, is so bad, so over-the-top, perhaps we should stick to the kiss that precedes it: “Oh God. He was so masterful, he was such a MAN!” which is squarely in Barbara Cartland territory. This is something new.

The thing about BJ in her first incarnation was that an awful lot of women could identify with her, chiefly the endearing insecurities. But Mrs Darcy’s sex life in this book isn’t necessarily going to resonate with women who have followed her faithfully from their thirties to their fifties. Bridget acquires a toyboy, 29 going on 30 to her 51. Sex is pretty well what the relationship is about, plus food and fart jokes. Roxster is not just terrifically fit but a sexual athlete, whose athleticism is matched all the way by Bridget, a tinderbox of desire after she’s lost a colossal amount of weight at the Obesity Clinic. And we’re made privy to an awful lot of the thrusts and stifled orgasms. So far from readers identifying with Bridget as born-again nymphomaniac (not my expression; her friend Tom’s), she may lose those who aren’t.

But if Bridget loses readers by dint of the sex it’ll be nothing to the numbers she alienates through her money. In the previous books, we weren’t really conscious about her income. But in this one, she doesn’t really work. She doesn’t have to. Mark Darcy, having been not just a top human rights lawyer but filthy rich with it, has left her provided for. “School fees, home, bills, income, all practical matters perfectly taken care of.” How nice. And how very unrepresentative of the rest of us; well, nearly all the rest of us. School fees? Her children’s prep school may be scope for satire — harridan mothers in SUVs and children with improbable Christian names (Spartacus? Eros?) — but it’s an inside-out view.

For those who loved her, there’s still a bit of the old Bridget to love. And one awaits any final instalment — BJ in old age — with interest. But in the years since the last book, Helen Fielding has changed, and so has Bridget. Less like us. Inevitable, I suppose, but a bit sad too.